1. The Field of the Invention
Exemplary embodiments of the present invention relate to the field of optical sub-assemblies, and more particularly, to optical sub-assemblies having a chip package that is coated with a resin.
2. The Relevant Technology
Transceiver modules come in a variety of shapes and sizes depending on the specific function they are designed to perform. Optoelectronic transceiver modules typically contain a transmitter optical sub-assembly (TOSA), a receiver optical sub-assembly (ROSA), and a printed circuit board (PCB) that controls the TOSA and ROSA. This PCB also connects the transceiver module to external devices using the various electrical circuits associated with the PCB.
Various standards setting organizations define the size and shape of optical transceivers. As with most electronic components, over the past several years the size of optical transceivers has been shrinking as electronics engineers fit more and more electrical circuitry into smaller and smaller packages. Unfortunately, as the number of electrical components and the tolerances between components on a PCB increases, and particularly as the density of these components increases, the manufacturing complexity and expense correspondingly increase.
PCBs are typically composed of a substrate, such as glass, plastic, or silicon, on which are printed or etched electrical circuits. In an attempt to alleviate the complexity and expense associated with filling one side of a PCB with circuits, designers can put circuits on both sides of the PCB. While this helps ease the premium on space, it even further complicates the manufacturing process.
Additionally, no matter how small PCBs become, they have limited space to receive electrical circuits. Also, the size of the PCB is limited by the size of the transceiver package; this size governed by industry standards. Even with sophisticated techniques to pack the most electrical circuitry possible onto the PCB, the physical space limitations presented by the device standards cannot be overcome. As the density of the circuitry increases, the costs of manufacture increase substantially.
Providing an optimal connection between a TOSA and/or a ROSA and a PCB can be difficult. For example, within a transceiver module, the TOSA and the ROSA must be positioned within small tolerances to achieve the desired optical performance. Similarly, the PCB must typically be precisely positioned for its connections to adjacent devices. Adding a third layer of rigid alignment requirements (the PCB to the TOSA and/or ROSA) makes accurately positioning the internal components difficult. Additionally, the TOSA and the ROSA often experience vibration and movement as optical cables are moved, attached, and detached. The PCB may be damaged or even crack if it rigidly attaches to the TOSA and/or ROSA at one end and a transceiver module housing at the other end. Thermal contraction or expansion can also cause problems if the devices are rigidly attached.
To eliminate some problems with manufacturing a transceiver, flexible circuits may be disposed between the TOSA and/or ROSA and the PCB. The flexible circuit electrically interconnects the TOSA, ROSA, and PCB while isolating the PCB from vibration, thermal expansion or contraction of the adjacent devices. During production, the PCB may be mechanically fixed in place while the TOSA and/or ROSA are free to move. Use of the flexible circuit accommodates for variations in device subassembly position and enables precise connection and alignment of the TOSA, ROSA, and the PCB.
To contain and protect the active devices of the TOSA and/or ROSA, the TOSA and/or ROSA include a transistor-outline (TO) header and associated cap. The TO header allows the electrical connection of the active devices in the TOSA and/or ROSA to the PCB, such as by way of a flexible circuit board or otherwise. With respect to their construction, TO headers often include a cylindrical metallic base with a number of conductive pins extending completely through, and generally perpendicular to, the base. One conventional method of conductively connecting a flexible circuit to a TO header includes pins on the TO header that connect to reinforced openings on one end of the flexible circuit, which are then soldered to affix the flexible circuit and ensure reliable connections. In turn, the other end of the flexible circuit attaches to “finger” like traces on the rigid PCB, via soldering or otherwise. Such soldered contacts are typically aligned in a linear row along the edge of the PCB.
The general construction of such an optoelectronic module 100 is shown in FIG. 1. Optoelectronic module 100 includes a TOSA 102 and a ROSA 104 that connect to a printed circuit board 106. A first flexible circuit 108 interconnects TOSA 102 and printed circuit board 106, while a second flexible circuit 110 interconnects ROSA 104 and printed circuit board 106. Also depicted as part of module 100 are housing 112 for containing the electrical components of module 100, Lucent Connector (LC) cable receptacles 116, or other fiber optic cable connectors such as standard connectors (SC), for receiving and securely attaching LC cables (not shown) to TOSA 102 and ROSA 104.
The entire optoelectronic module 100 connects to a computer system that controls the operation of the transceiver module. The computer system, such as a host system, can direct module 100 to transmit an optical signal by directing an electronic signal through PCB 106 and into TOSA 102. The TOSA 102 then generates an optical signal via an internal laser or light emitting diode (LED) that propagates into an outgoing optical cable at port 116. Similarly, ROSA 104 receives an optical signal via a photodiode from the incoming optical cable at port 116 and transmits the signal to PCB 106 and on to the computer system. Specific details of the connection of flexible circuits to PCBs can be found in co-pending and co-owned U.S. patent application Ser. No. 10/409,837, filed on Apr. 9, 2003 and entitled “Flexible Circuit for Establishing Electrical Connectivity with Optical Sub-Assembly”, which is incorporated herein by reference in its entirety.
One problem associated with the design shown in FIG. 1 is that the connections between flex circuit 108, PCB 106, and TOSA 102 can be difficult and time consuming to make. Likewise, the connections between flex circuit 110, PCB 106 and ROSA 104 can also be difficult and time consuming to make. This increased time and complexity greatly increases the cost of the modules as a whole.